U.S. patent application number 13/144015 was filed with the patent office on 2012-01-26 for liquid crystal display device.
Invention is credited to Kaori Saitoh, Yasutoshi Tasaka.
Application Number | 20120019437 13/144015 |
Document ID | / |
Family ID | 42316526 |
Filed Date | 2012-01-26 |
United States Patent
Application |
20120019437 |
Kind Code |
A1 |
Tasaka; Yasutoshi ; et
al. |
January 26, 2012 |
LIQUID CRYSTAL DISPLAY DEVICE
Abstract
A liquid crystal display device (100) according to the present
invention includes an active matrix substrate (120) including a
plurality of pixel electrodes (124) provided in a matrix of a
plurality of rows by a plurality columns; a counter substrate (140)
including a counter electrode (144); a vertical alignment type
liquid crystal layer (160); and axis-symmetrical liquid crystal
domain formation portions (150) each for forming a liquid crystal
domain in which liquid crystal molecules (162) in the liquid
crystal layer (160) are aligned in axis symmetry, the
axis-symmetrical liquid crystal domain formation portions (150)
each being located at the center of the respective liquid crystal
domain. The plurality of pixel electrodes (124) each define a pixel
area. The axis-symmetrical liquid crystal domain formation portions
(150) are each provided in correspondence with an area between two
pixel areas defined by two pixel electrodes (124) adjacent to each
other.
Inventors: |
Tasaka; Yasutoshi; (Osaka,
JP) ; Saitoh; Kaori; (Osaka, JP) |
Family ID: |
42316526 |
Appl. No.: |
13/144015 |
Filed: |
January 8, 2010 |
PCT Filed: |
January 8, 2010 |
PCT NO: |
PCT/JP2010/000079 |
371 Date: |
July 11, 2011 |
Current U.S.
Class: |
345/87 |
Current CPC
Class: |
G02F 1/133707
20130101 |
Class at
Publication: |
345/87 |
International
Class: |
G09G 3/36 20060101
G09G003/36 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 9, 2009 |
JP |
2009-004093 |
Claims
1. A liquid crystal display device, comprising: an active matrix
substrate including a plurality of pixel electrodes provided in a
matrix of a plurality of rows by a plurality columns; a counter
substrate including a counter electrode; a vertical alignment type
liquid crystal layer provided between the active matrix substrate
and the counter substrate; and a plurality of axis-symmetrical
liquid crystal domain formation portions each for forming a liquid
crystal domain in which liquid crystal molecules in the liquid
crystal layer are aligned in axis symmetry, the plurality of
axis-symmetrical liquid crystal domain formation portions each
being located at a center of the respective liquid crystal domain;
wherein: the plurality of pixel electrodes each define a pixel
area; and at least one axis-symmetrical liquid crystal domain
formation portion among the plurality of axis-symmetrical liquid
crystal domain formation portions is provided in correspondence
with an area between two pixel areas defined by two pixel
electrodes adjacent to each other among the plurality of pixel
electrodes or in correspondence with an area surrounded by four
pixel areas defined by four pixel electrodes arranged in two rows
by two columns among the plurality of pixel electrodes.
2. The liquid crystal display device of claim 1, wherein the
plurality of axis-symmetrical liquid crystal domain formation
portions include a plurality of convexed portions provided on a
liquid crystal layer side of at least one of the active matrix
substrate and the counter substrate, or a plurality of
electrode-absent portions provided in at least one of the counter
electrode and the two or four pixel electrodes among the plurality
of pixel electrodes.
3. The liquid crystal display device of claim 2, wherein the
plurality of convexed portions are provided on the liquid crystal
layer side of at least one of the active matrix substrate and the
counter substrate.
4. The liquid crystal display device of claim 2, wherein the
plurality of electrode-absent portions are provided in at least one
of the counter electrode and the plurality of pixel electrodes.
5. The liquid crystal display device of claim 1, wherein at least
one axis-symmetrical liquid crystal domain formation portion among
the plurality of axis-symmetrical liquid crystal domain formation
portions is provided in correspondence with an area between two
pixel areas defined by two pixel electrodes adjacent to each other
among the plurality of pixel electrodes.
6. The liquid crystal display device of claim 5, wherein the two
pixel areas are adjacent to each other in the column direction.
7. The liquid crystal display device of claim 1, wherein at least
one axis-symmetrical liquid crystal domain formation portion among
the plurality of axis-symmetrical liquid crystal domain formation
portions is provided in correspondence with an area surrounded by
four pixel areas defined by four pixel electrodes arranged in two
rows by two columns among the plurality of pixel electrodes.
8. The liquid crystal display device of claim 1, wherein: the
plurality of pixel electrodes include first, second and third pixel
electrodes sequentially arranged in a prescribed direction; and the
plurality of axis-symmetrical liquid crystal domain formation
portions include a first axis-symmetrical liquid crystal domain
formation portion provided in correspondence with an area between
two pixel areas defined by the first pixel electrode and the second
pixel electrode, and a second axis-symmetrical liquid crystal
domain formation portion provided in correspondence with an area
between two pixel areas defined by the second pixel electrode and
the third pixel electrode.
9. The liquid crystal display device of claim 1, wherein: the
plurality of pixel electrodes include first, second, third, fourth,
fifth and sixth pixel electrodes arranged in three rows by two
columns; and the plurality of axis-symmetrical liquid crystal
domain formation portions include a first axis-symmetrical liquid
crystal domain formation portion provided in correspondence with an
area surrounded by four pixel areas defined by the first, second,
third and fourth pixel electrodes, and a second axis-symmetrical
liquid crystal domain formation portion provided in correspondence
with an area surrounded by four pixel areas defined by the third,
fourth, fifth and sixth pixel electrodes.
10. The liquid crystal display device of claim 1, wherein the at
least one axis-symmetrical liquid crystal domain formation portion
overlaps each of the two pixel electrodes or each of the four pixel
electrodes by 9 .mu.m or more.
11. The liquid crystal display device of claim 1, wherein: the
pixel areas respectively defined by the plurality of pixel
electrodes each include a transmissive region and a reflective
region; in the two pixel areas or the four pixel areas, one type of
regions among the transmissive regions and the reflective regions
are provided so as to face each other; and the at least one
axis-symmetrical liquid crystal domain formation portion is
provided in correspondence with an area between the two pixel areas
or an area surrounded by the four pixel areas.
12. A liquid crystal display device, comprising: an active matrix
substrate including a plurality of pixel electrodes provided in a
matrix of a plurality of rows by a plurality columns; a counter
substrate including a counter electrode; and a vertical alignment
type liquid crystal layer provided between the active matrix
substrate and the counter substrate; wherein: the plurality of
pixel electrodes include a first pixel electrode and a second pixel
electrode adjacent to the first pixel electrode; the first pixel
electrode includes a first trunk electrode and a plurality of first
linear electrodes extending parallel to each other in a first
direction from the first trunk electrode, and a plurality of second
linear electrodes extending parallel to each other in a second
direction, crossing perpendicularly the first direction, from the
first trunk electrode; the second pixel electrode includes a second
trunk electrode and a plurality of third linear electrodes
extending parallel to each other in a third direction, antiparallel
to the second direction, from the second trunk electrode, and a
plurality of fourth linear electrodes extending parallel to each
other in a fourth direction, antiparallel to the first direction,
from the second trunk electrode; and the liquid crystal layer
includes a first liquid crystal domain formed by the first linear
electrodes of the first pixel electrode, a second liquid crystal
domain formed by the second linear electrodes of the first pixel
electrode, a third liquid crystal domain formed by the third linear
electrodes of the second pixel electrode, and a fourth liquid
crystal domain formed by the fourth linear electrodes of the second
pixel electrode.
13. The liquid crystal display device of claim 12, wherein the
first pixel electrode and the second pixel electrode are adjacent
to each other in the column direction.
14. A liquid crystal display device, comprising: an active matrix
substrate including a plurality of pixel electrodes provided in a
matrix of a plurality of rows by a plurality columns; a counter
substrate including a counter electrode; and a vertical alignment
type liquid crystal layer provided between the active matrix
substrate and the counter substrate; wherein: the plurality of
pixel electrodes include a first pixel electrode, a second pixel
electrode, a third pixel electrode and a fourth pixel electrode
arranged in two rows by two columns; the first pixel electrode
includes a plurality of first linear electrodes extending parallel
to each other in a first direction; the second pixel electrode
includes a plurality of second linear electrodes extending parallel
to each other in a second direction crossing perpendicularly the
first direction; the third pixel electrode includes a plurality of
third linear electrodes extending parallel to each other in a third
direction antiparallel to the second direction; the fourth pixel
electrode includes a plurality of fourth linear electrodes
extending parallel to each other in a fourth direction antiparallel
to the first direction; and the liquid crystal layer includes a
first liquid crystal domain formed by the first pixel electrode, a
second liquid crystal domain formed by the second pixel electrode,
a third liquid crystal domain formed by the third pixel electrode,
and a fourth liquid crystal domain formed by the fourth pixel
electrode.
15. The liquid crystal display device of claim 1, wherein the
active matrix substrate further includes gate lines extending
parallel to the plurality of rows.
16. The liquid crystal display device of claim 15, wherein the gate
lines are each provided between the pixel electrodes of two rows
adjacent to each other among the plurality of rows.
17. The liquid crystal display device of claim 15, wherein the
active matrix substrate further includes storage capacitance lines
extending parallel to the plurality of rows.
18. The liquid crystal display device of claim 17, wherein one type
of lines among the gate lines and the storage capacitance lines are
each provided between the pixel electrodes of two rows adjacent to
each other among the plurality of rows.
19. The liquid crystal display device of claim 18, wherein the
other type of lines among the gate lines and the storage
capacitance lines each overlap the pixel electrodes of one of the
two rows.
20. The liquid crystal display device of claim 19, wherein the
other type of lines each overlap centers of the pixel electrodes of
the one of the two rows.
21. The liquid crystal display device of claim 19, wherein the
other type of lines each overlap portions, other than the centers,
of the pixel electrodes of the one of the two rows.
Description
TECHNICAL FIELD
[0001] The present invention relates to a liquid crystal display
device.
BACKGROUND ART
[0002] Liquid crystal display devices are used as, for example,
small display devices such as display sections of mobile phones in
addition to display sections of large-screen TVs. TN (Twisted
Nematic) mode liquid crystal display devices often used
conventionally have a relatively narrow viewing angle. Recently,
however, wide viewing angle liquid crystal display devices of an
IPS (In-Plane-Switching) mode, a VA (Vertical Alignment) mode and
the like have been produced. Among such wide viewing angle modes,
the VA mode can realize a high contrast ratio and so is adopted for
many liquid crystal display devices.
[0003] As one type of VA mode, a CPA (Continuous Pinwheel Alignment
mode is known. In a general CPA mode liquid crystal display device,
pixel electrodes and unit electrodes having a highly symmetrical
shape are provided, and also projections (convexed portions) or
openings are provided in correspondence with the centers of the
pixel electrodes or the unit electrodes. When a voltage is applied
to a liquid crystal layer, liquid crystal molecules are
tilt-aligned radially in accordance with an oblique electric field
formed by a counter electrode and the highly symmetrical pixel
electrodes or unit electrodes. Using the oblique electric field
formed by an alignment regulating force of the inclined side
surface of the convexed portions or by the openings, the tilted
alignment of the liquid crystal molecules is stabilized. Thus,
liquid crystal domains centering around the projections (convexed
portions) or the openings are formed. In this manner, with a CPA
mode liquid crystal display device, the liquid crystal molecules
are aligned radially in an attempt to improve the viewing angle
characteristics (see, for example, Patent Documents 1 through
3).
[0004] In a liquid crystal display device disclosed in Patent
Document 1, pixel electrodes are provided in areas defined by gate
lines and source lines, and the pixel electrodes each have a
plurality of subpixel electrodes (unit electrodes) separated from
each other. Storage capacitance lines extending parallel to the
gate lines are provided in areas between the plurality subpixel
electrodes. A counter electrode includes convexed portions in
correspondence with the respective centers of the plurality of
subpixel electrodes in an attempt to improve the viewing angle
characteristics.
[0005] In a liquid crystal display device disclosed in Patent
Document 2, pixel electrodes are provided so as to overlap gate
lines, and storage capacitance lines extending parallel to the gate
lines are each provided between two pixel electrodes adjacent to
each other in a column direction. In the liquid crystal display
device of Patent Document 2, the pixel electrodes each have a
plurality of unit electrodes connected to each other, and a counter
substrate includes convexed portions in correspondence with the
respective centers of the unit electrodes.
[0006] Patent Document 3 discloses a transreflective liquid crystal
display device. In the liquid crystal display device of Patent
Document 3, a counter substrate includes convexed portions in
correspondence with the respective centers of transmissive regions
and reflective regions. In the liquid crystal display device of
Patent Document 3, a liquid crystal layer is thicker in the
reflective regions than in the transmissive regions. Owing to this,
the retardation amount in the reflective regions is approximately
equal to the retardation amount in the transmissive regions. In the
liquid crystal display device of Patent Document 3, the convexed
portions provided in the transmissive regions are higher than the
convexed portions provided in the reflective regions. Owing to
this, the alignment stability and the response speed of the liquid
crystal molecules in the respective regions are improved.
[0007] As another type of VA mode, an MVA (Multi-domain Vertical
Alignment) mode, by which a plurality of liquid crystal domains are
formed in one pixel area, is also known. In an MVA mode liquid
crystal display device, alignment regulating structures provided on
the liquid crystal layer side of at least one of a pair of
substrates which face each other with a vertical alignment type
liquid crystal layer interposed therebetween. The alignment
regulating structure is, for example, a linear slit (opening) or a
rib (projecting structure) provided on an electrode. Owing to the
alignment regulating structures, an alignment regulating force is
supplied from one side or both of two sides of the liquid crystal
layer, and so a plurality of liquid crystal domains (typically,
four liquid crystal domains) having different alignment directions
are formed. In this manner, it is attempted to improve the viewing
angle characteristics (see, for example, Patent Document 4).
[0008] However, in the liquid crystal display device of Patent
Document 4, the alignment regulating force is supplied to liquid
crystal molecules by the linear slits or the ribs. Therefore, the
alignment regulating force acting on the liquid crystal molecules
in the pixel areas varies in accordance with the distance from the
slit or the rib. As a result, the response speed of the liquid
crystal molecules in the pixels varies. For this reason, a VA mode
liquid crystal display device in which the alignment regulating
force is supplied to the liquid crystal molecules within a plane of
the pixel electrodes by forming the pixel electrodes in a specific
shape has been studied (see, for example, Patent Document 5).
[0009] In the liquid crystal display device of Patent Document 5,
the pixel electrodes having a minute linear pattern (striped
pattern) are provided. The linear pattern includes a cross-shaped
trunk electrode and linear electrodes extending in four different
directions from the trunk electrode. Such a structure of the pixel
electrode is called the "fishbone structure". Storage capacitance
lines are each provided so as to overlap a part of the cross-shaped
trunk electrode. With the liquid crystal display device of Patent
Document 5, when a voltage is applied to a liquid crystal layer,
the liquid crystal molecules are aligned parallel to the
longitudinal direction of the striped pattern. As a result, a
plurality of liquid crystal domains (typically, four liquid crystal
domains) having different alignment directions are formed. In this
manner, it is attempted to improve the viewing angle
characteristics.
CITATION LIST
Patent Literature
[0010] Patent Document 1: Japanese Laid-Open Patent Publication No.
2007-316234 [0011] Patent Document 2: Japanese Laid-Open Patent
Publication No. 2007-128094 [0012] Patent Document 3: Japanese
Laid-Open Patent Publication No. 2006-126228 [0013] Patent Document
4: Japanese Laid-Open Patent Publication No. 11-242225 [0014]
Patent Document 5: Japanese Laid-Open Patent Publication No.
2003-149647
SUMMARY OF INVENTION
Technical Problem
[0015] Recently, liquid crystal display devices are desired to have
a higher luminance. However, a pixel may occasionally include an
area providing a low luminance when a voltage is applied to the
liquid crystal layer. For example, in a CPA mode liquid crystal
display device, the liquid crystal molecules corresponding to the
convexed portions or the openings are aligned generally vertically
to a main surface of an alignment film even in the presence of a
voltage, and the luminance in such an area is lower than that in
the other areas. In a liquid crystal display device of the fishbone
structure, the liquid crystal molecules in the vicinity of the
trunk electrode are not aligned in a prescribed alignment direction
even in the presence of a voltage, and the luminance in such an
area is lower than that in the other areas.
[0016] When a pixel includes an area providing a lower luminance,
it is difficult to provide a liquid crystal display devices of a
higher luminance. Especially, liquid crystal display devices are
recently desired to be improved in precision. As the precision is
more improved, the size of each pixel is decreased. In a CPA mode
liquid crystal display device, when the size of the convexed
portions is decreased in accordance with the decrease in the size
of the pixels, the response speed and the alignment stability are
lowered. When the size of the pixel electrodes is decreased without
changing the size of the convexed portions, the substantial
aperture area size in the pixels is decreased. In a liquid crystal
display device of the fishbone structure, the width of the trunk
electrode cannot be decreased to a level less than the production
limit. Therefore, when the size of the pixel electrodes is
decreased, the substantial aperture area size in the pixels is
decreased.
[0017] The present invention made in light of the above-described
problems has an object of providing a liquid crystal display device
suitable to the improvement of the luminance.
Solution to Problem
[0018] A liquid crystal display device according to the present
invention includes an active matrix substrate including a plurality
of pixel electrodes provided in a matrix of a plurality of rows by
a plurality columns; a counter substrate including a counter
electrode; a vertical alignment type liquid crystal layer provided
between the active matrix substrate and the counter substrate; and
a plurality of axis-symmetrical liquid crystal domain formation
portions each for forming a liquid crystal domain in which liquid
crystal molecules in the liquid crystal layer are aligned in axis
symmetry, the plurality of axis-symmetrical liquid crystal domain
formation portions each being located at a center of the respective
liquid crystal domain. The plurality of pixel electrodes each
define a pixel area; and at least one axis-symmetrical liquid
crystal domain formation portion among the plurality of
axis-symmetrical liquid crystal domain formation portions is
provided in correspondence with an area between two pixel areas
defined by two pixel electrodes adjacent to each other among the
plurality of pixel electrodes or in correspondence with an area
surrounded by four pixel areas defined by four pixel electrodes
arranged in two rows by two columns among the plurality of pixel
electrodes.
[0019] In one embodiment, the plurality of axis-symmetrical liquid
crystal domain formation portions include a plurality of convexed
portions provided on a liquid crystal layer side of at least one of
the active matrix substrate and the counter substrate, or a
plurality of electrode-absent portions provided in at least one of
the counter electrode and the two or four pixel electrodes among
the plurality of pixel electrodes.
[0020] In one embodiment, the plurality of convexed portions are
provided on the liquid crystal layer side of at least one of the
active matrix substrate and the counter substrate.
[0021] In one embodiment, the plurality of electrode-absent
portions are provided in at least one of the counter electrode and
the plurality of pixel electrodes.
[0022] In one embodiment, at least one axis-symmetrical liquid
crystal domain formation portion among the plurality of
axis-symmetrical liquid crystal domain formation portions is
provided in correspondence with an area between two pixel areas
defined by two pixel electrodes adjacent to each other among the
plurality of pixel electrodes.
[0023] In one embodiment, the two pixel areas are adjacent to each
other in the column direction.
[0024] In one embodiment, at least one axis-symmetrical liquid
crystal domain formation portion among the plurality of
axis-symmetrical liquid crystal domain formation portions is
provided in correspondence with an area surrounded by four pixel
areas defined by four pixel electrodes arranged in two rows by two
columns among the plurality of pixel electrodes.
[0025] In one embodiment, the plurality of pixel electrodes include
first, second and third pixel electrodes sequentially arranged in a
prescribed direction; and the plurality of axis-symmetrical liquid
crystal domain formation portions include a first axis-symmetrical
liquid crystal domain formation portion provided in correspondence
with an area between two pixel areas defined by the first pixel
electrode and the second pixel electrode, and a second
axis-symmetrical liquid crystal domain formation portion provided
in correspondence with an area between two pixel areas defined by
the second pixel electrode and the third pixel electrode.
[0026] In one embodiment, the plurality of pixel electrodes include
first, second, third, fourth, fifth and sixth pixel electrodes
arranged in three rows by two columns; and the plurality of
axis-symmetrical liquid crystal domain formation portions include a
first axis-symmetrical liquid crystal domain formation portion
provided in correspondence with an area surrounded by four pixel
areas defined by the first, second, third and fourth pixel
electrodes, and a second axis-symmetrical liquid crystal domain
formation portion provided in correspondence with an area
surrounded by four pixel areas defined by the third, fourth, fifth
and sixth pixel electrodes.
[0027] In one embodiment, the at least one axis-symmetrical liquid
crystal domain formation portion overlaps each of the two pixel
electrodes or each of the four pixel electrodes by 9 .mu.m or
more.
[0028] In one embodiment, the pixel areas respectively defined by
the plurality of pixel electrodes each include a transmissive
region and a reflective region; in the two pixel areas or the four
pixel areas, one type of regions among the transmissive regions and
the reflective regions are provided so as to face each other; and
the at least one axis-symmetrical liquid crystal domain formation
portion is provided in correspondence with an area between the two
pixel areas or an area surrounded by the four pixel areas.
[0029] A liquid crystal display device according to the present
invention includes an active matrix substrate including a plurality
of pixel electrodes provided in a matrix of a plurality of rows by
a plurality columns; a counter substrate including a counter
electrode; and a vertical alignment type liquid crystal layer
provided between the active matrix substrate and the counter
substrate. The plurality of pixel electrodes include a first pixel
electrode and a second pixel electrode adjacent to the first pixel
electrode; the first pixel electrode includes a first trunk
electrode and a plurality of first linear electrodes extending
parallel to each other in a first direction from the first trunk
electrode, and a plurality of second linear electrodes extending
parallel to each other in a second direction, crossing
perpendicularly the first direction, from the first trunk
electrode; the second pixel electrode includes a second trunk
electrode and a plurality of third linear electrodes extending
parallel to each other in a third direction, antiparallel to the
second direction, from the second trunk electrode, and a plurality
of fourth linear electrodes extending parallel to each other in a
fourth direction, antiparallel to the first direction, from the
second trunk electrode; and the liquid crystal layer includes a
first liquid crystal domain formed by the first linear electrodes
of the first pixel electrode, a second liquid crystal domain formed
by the second linear electrodes of the first pixel electrode, a
third liquid crystal domain formed by the third linear electrodes
of the second pixel electrode, and a fourth liquid crystal domain
formed by the fourth linear electrodes of the second pixel
electrode.
[0030] In one embodiment, the first pixel electrode and the second
pixel electrode are adjacent to each other in the column
direction.
[0031] A liquid crystal display device according to the present
invention includes an active matrix substrate including a plurality
of pixel electrodes provided in a matrix of a plurality of rows by
a plurality columns; a counter substrate including a counter
electrode; and a vertical alignment type liquid crystal layer
provided between the active matrix substrate and the counter
substrate. The plurality of pixel electrodes include a first pixel
electrode, a second pixel electrode, a third pixel electrode and a
fourth pixel electrode arranged in two rows by two columns; the
first pixel electrode includes a plurality of first linear
electrodes extending parallel to each other in a first direction;
the second pixel electrode includes a plurality of second linear
electrodes extending parallel to each other in a second direction
crossing perpendicularly the first direction; the third pixel
electrode includes a plurality of third linear electrodes extending
parallel to each other in a third direction antiparallel to the
second direction; the fourth pixel electrode includes a plurality
of fourth linear electrodes extending parallel to each other in a
fourth direction antiparallel to the first direction; and the
liquid crystal layer includes a first liquid crystal domain formed
by the first pixel electrode, a second liquid crystal domain formed
by the second pixel electrode, a third liquid crystal domain formed
by the third pixel electrode, and a fourth liquid crystal domain
formed by the fourth pixel electrode.
[0032] In one embodiment, the active matrix substrate further
includes gate lines extending parallel to the plurality of
rows.
[0033] In one embodiment, the gate lines are each provided between
the pixel electrodes of two rows adjacent to each other among the
plurality of rows.
[0034] In one embodiment, the active matrix substrate further
includes storage capacitance lines extending parallel to the
plurality of rows.
[0035] In one embodiment, one type of lines among the gate lines
and the storage capacitance lines are each provided between the
pixel electrodes of two rows adjacent to each other among the
plurality of rows.
[0036] In one embodiment, the other type of lines among the gate
lines and the storage capacitance lines each overlap the pixel
electrodes of one of the two rows.
[0037] In one embodiment, the other type of lines each overlap
centers of the pixel electrodes of the one of the two rows.
[0038] In one embodiment, the other type of lines each overlap
portions, other than the centers, of the pixel electrodes of the
one of the two rows.
Advantageous Effects of Invention
[0039] The present invention can provide a liquid crystal display
device suitable to the improvement of the luminance.
BRIEF DESCRIPTION OF DRAWINGS
[0040] FIG. 1(a) is a schematic view of a liquid crystal display
device in Embodiment 1 according to the present invention, and FIG.
1(b) is a schematic plan view thereof.
[0041] FIG. 2 is a schematic view of one convexed portion and the
vicinity thereof in the liquid crystal display device shown in FIG.
1.
[0042] FIG. 3(a) is a schematic view of a liquid crystal display
device in Comparative Example 1, and FIG. 3(b) is a schematic plan
view thereof.
[0043] FIG. 4 is a schematic plan view of a liquid crystal display
device in a modified example of Embodiment 1.
[0044] FIG. 5(a) is a schematic view of a liquid crystal display
device in Embodiment 2 according to the present invention, and FIG.
5(b) is a schematic plan view thereof.
[0045] FIG. 6 is an enlarged schematic view of the liquid crystal
display device shown in FIG. 5.
[0046] FIG. 7 is a schematic view of a liquid crystal display
device in Embodiment 3 according to the present invention.
[0047] FIG. 8 is a schematic view of convexed portions and the
vicinity thereof in the liquid crystal display device shown in FIG.
7.
[0048] FIG. 9 is a schematic view of a liquid crystal display
device in a modified example of Embodiment 3.
[0049] FIG. 10 is a schematic view of a liquid crystal display
device in another modified example of Embodiment 3.
[0050] FIG. 11 is a schematic view of a liquid crystal display
device in still another modified example of Embodiment 3.
[0051] FIG. 12 is a schematic view of a liquid crystal display
device in still another modified example of Embodiment 3.
[0052] FIG. 13 is a schematic view of a liquid crystal display
device in still another modified example of Embodiment 3.
[0053] FIG. 14(a) is a schematic view of a liquid crystal display
device in Embodiment 4 according to the present invention, and FIG.
14(b) is a schematic plan view thereof.
[0054] FIG. 15(a) is a schematic view of a liquid crystal display
device in Comparative Example 2, and FIG. 15(b) is a schematic plan
view thereof.
[0055] FIG. 16 is a schematic view showing lines in the liquid
crystal display device shown in FIG. 14.
[0056] FIG. 17 is a schematic view of a liquid crystal display
device in a modified example of Embodiment 4.
DESCRIPTION OF EMBODIMENTS
[0057] Hereinafter, liquid crystal display devices in embodiments
according to the present invention will be described with reference
to the drawings. The present invention is not limited to the
following embodiments.
Embodiment 1
[0058] Hereinafter, a liquid crystal display device in Embodiment 1
according to the present invention will be described with reference
to FIG. 1. FIG. 1(a) is a schematic view of a liquid crystal
display device 100A in this embodiment, and FIG. 1(b) is a plan
view of the liquid crystal display device 100A.
[0059] The liquid crystal display device 100A includes an active
matrix substrate 120 including pixel electrodes 124 provided on an
insulating plate 122, a counter substrate 140 including a counter
electrode 144 provided on an insulating plate 142, and a liquid
crystal layer 160 provided between the active matrix substrate 120
and the counter substrate 140. The liquid crystal display device
100A is of a CPA mode.
[0060] The active matrix substrate 120 and the counter substrate
140 each have an alignment film and a polarizer plate, neither of
which is shown. The polarization axes of the polarizer plates have
a crossed Nicols relationship. The liquid crystal display device
100A is, for example, of a transmissive type and may further
include a backlight (not shown).
[0061] The liquid crystal display device 100A includes a plurality
of pixels arranged in a matrix of a plurality of rows by a
plurality of columns. For example, in a liquid crystal display
device which provides color display using primary colors of R
(red), G (green) and B (blue), one color is represented by three
pixels of R, G and B. The pixel electrodes 124 each define a pixel
area.
[0062] The liquid crystal display device 100A operates in a VA
mode. The alignment films (not shown) are vertical alignment films,
and the liquid crystal layer 160 is a vertical alignment type
liquid crystal layer. Liquid crystal molecules 162 have a negative
anisotropy, and display in a normally black mode is provided by the
liquid crystal molecules 162 in combination with the polarizer
plates located in the crossed Nicols relationship. The liquid
crystal layer 160 may contain a chiral agent.
[0063] Herein, the active matrix substrate 120 and the counter
substrate 140 each have the alignment film. Alternatively, at least
one of the active matrix substrate 120 and the counter substrate
140 may have the alignment film. It is preferable, however, that
both of the active matrix substrate 120 and the counter substrate
140 each have the alignment film from the viewpoint of the
alignment stability. The counter substrate 140 includes a color
filter and a black matrix.
[0064] The liquid crystal display device 100A further includes an
axis-symmetrical liquid crystal domain formation portion 150 for
forming a liquid crystal domain in which the liquid crystal
molecules 162 in the liquid crystal layer 160 are aligned in axis
symmetry (C.infin.), and is positioned at the center of the liquid
crystal domain. In the liquid crystal display device 100A, convexed
portions 152 are provided as the axis-symmetrical liquid crystal
domain formation portions 150 on the liquid crystal layer 160 side
of the counter substrate 140. The convexed portions 152 are also
called "rivets".
[0065] When no voltage is applied to the liquid crystal layer 160
or when the voltage applied thereto is relatively low, the liquid
crystal molecules 162 are aligned vertically to a main surface of
the alignment film (not shown) except for a part of the liquid
crystal molecules 162 which are located in the vicinity of the
convexed portions 152. By contrast, when a prescribed voltage is
applied to the liquid crystal layer 160, the liquid crystal
molecules 162 are tilt-aligned in axis symmetry around each
convexed portion 152 as the center. Thus, the axis-symmetrical
liquid crystal domains are formed.
[0066] FIG. 1(b) schematically show the pixels in the liquid
crystal display device 100A. FIG. 1(b) shows the pixels arranged in
four rows by four columns. For example, each pixel 124 has a length
of 30 .mu.m in an x direction and a length of 90 .mu.m in a y
direction.
[0067] The active matrix substrate 120 of the liquid crystal
display device 100A includes gate lines G extending in the x
direction and source lines S extending in the y direction. In the
vicinity of intersections of the gate lines G and the source lines
S, TFTs (not shown) are provided. The gate lines G each extend
between the pixel electrodes 124 of two rows adjacent to each
other, and the source lines S each extend between the pixel
electrodes 124 of two columns adjacent to each other. For example,
the gate lines G and the source lines S each have a width of 4
.mu.m. When necessary, storage capacitance lines (not shown in FIG.
1(b)) may be provided. The black matrix (not shown) may be provided
so as to overlap the gate lines G, the source lines S and the
storage capacitance lines. In the liquid crystal display device
100A, the convexed portions 152 are provided so as to overlap every
other gate lines G.
[0068] Now, attention will be paid to two pixel electrodes adjacent
to each other in the column direction. Among the two pixel
electrodes, one is represented by reference sign 124a and the other
is represented by reference sign 124b. Among the convexed portions
152, the convexed portion provided in correspondence with an area
between two pixel areas defined by the two pixel electrodes 124a
and 124b is represented by reference sign 152a.
[0069] In the liquid crystal display device 100A, the convexed
portion 152a is provided in correspondence with the area between
the pixel areas defined by the two pixel electrodes 124a and 124b,
and the convexed portion 152a partially overlaps each of the pixel
electrodes 124a and 124b. For example, the convexed portion 152a is
a projection having a circular bottom surface of a diameter of 15
.mu.m, and the distance between the pixel electrode 124a and the
pixel electrode 124b is 5 .mu.m. In this case, an overlapping width
(maximum width) of the convexed portion 152a and the pixel
electrode 124a is 5 .mu.m; and similarly, an overlapping width
(maximum width) of the convexed portion 152a and the pixel
electrode 124b is 5 .mu.m. The bottom surface of the convexed
portion 152a may be elliptical.
[0070] FIG. 2 shows an enlarged view of pixels in the liquid
crystal display device 100A. FIG. 2 shows the pixels arranged in
four rows by two columns. As described above, in the liquid crystal
display device 100A, the convexed portion 152a is provided in
correspondence with the area between the two pixel electrodes 124a
and 124b. When a prescribed voltage is applied, the liquid crystal
molecules 162 in the two pixel areas corresponding to the pixel
electrodes 124a and 124b are tilt-aligned in axis symmetry around
the convexed portion 152a as the center. Specifically, when a
prescribed voltage is applied, the liquid crystal molecules 162
corresponding to the pixel electrode 124a are aligned in
correspondence with a +y side part of the convexed portion 152a,
and the liquid crystal molecules 162 corresponding to the pixel
electrode 124b are aligned in correspondence with a -y side part of
the convexed portion 152a. In this manner, when a voltage is
applied, a liquid crystal domain is formed around the convexed
portion 152a as the center. In this specification, the center of
the symmetrical alignment of the liquid crystal molecules 162 will
be referred to as the "alignment center". In the liquid crystal
display device 100A, the convexed portions 152 are alignment
centers of the liquid crystal molecules 162. In this manner, the
liquid crystal molecules 162 corresponding to the two pixel
electrodes 124a and 124b are aligned around the convexed portion
152a as the center, and owing to this, the viewing angle
characteristics are improved. As described later, it is preferable
that the convexed portion 152a is provided so as to overlap each of
the pixel electrodes 124a and 124b by 9 .mu.m or more.
[0071] Hereinafter, advantages of the liquid crystal display device
100A in this embodiment will be described in comparison with a
liquid crystal display device in Comparative Example 1. First, with
reference to FIG. 3, a liquid crystal display device 800 in
Comparative Example 1 will be described. FIG. 3(a) is a schematic
view of the liquid crystal display device 800, and FIG. 3(b) is a
plan view of the liquid crystal display device 800.
[0072] A counter substrate 840 of the liquid crystal display device
800 includes convexed portions 852 each located in correspondence
with the center of a pixel area defined by each pixel electrode
824. When a voltage is applied to a liquid crystal layer 860,
liquid crystal molecules 862 are tilt-aligned in axis symmetry
around the convexed portions 852 as the centers.
[0073] In such a liquid crystal display device 800, when a voltage
is applied to the liquid crystal layer 860, the liquid crystal
molecules 862 corresponding to the convexed portions 852 are
aligned generally vertically to a main surface of an alignment
film. Therefore, the luminance of the areas corresponding to the
convexed portions 852 is lower than the luminance of the other
areas. For example, in the case where the convexed portions 852
have a diameter .phi. of 15 .mu.m, when the luminance of the entire
areas corresponding to the convexed portions 852 is the minimum
level, the size of the area where optical loss is caused by the
convexed portion 852 in one pixel is 177 .mu.m.sup.2. The
substantial numerical aperture of the pixel corresponds to a value
obtained by subtracting the size of this area from the area size of
the pixel electrode 824. When the size of the pixel electrodes 824
is decreased, the influence as described above is more conspicuous.
When the size of the convexed portions 852 is decreased in
accordance with the decrease in the size of the pixel electrodes
824, the response speed and the alignment stability are lowered.
When the size of the pixel electrodes 824 is decreased without
changing the size of the convexed portions 852, the area size of
the openings in the pixels is decreased and also the ratio of the
convexed portions 852 of the lower luminance is increased. As a
result, the luminance is significantly lowered.
[0074] By contrast, in the liquid crystal display device 100A in
this embodiment, the convexed portions 152 are each provided in
correspondence with the area between the pixel areas defined by the
pixel electrodes 124a and 124b. Each convexed portion 152 only
partially overlaps the pixel electrodes 124a and 124b, but the
remaining part of the convexed portion 152 does not overlap the
pixel electrodes 124a or 124b. Therefore, under the conditions that
the convexed portions 152 each have a diameter .phi. of 15 .mu.m,
gate lines G each have a width of 4 .mu.m, and the distance between
the pixel electrodes 124a and 124b is 4 .mu.m; a sum of the
overlapping area size of the convexed portion 152a and the pixel
electrode 124a and the overlapping area size of the convexed
portion 152a and the pixel electrode 124b is 117 .mu.m.sup.2. As
can be seen from this, the liquid crystal display device 100A in
this embodiment can suppress the decrease in the substantial
numerical aperture and thus can realize a high luminance.
[0075] In the liquid crystal display device 800 in Comparative
Example 1, symmetrical viewing angle characteristics are realized
in each pixel. By contrast, in the liquid crystal display device
100A, symmetrical viewing angle characteristics are realized in
every other pixels. Therefore, with the liquid crystal display
device 100A, when, for example, special display of lighting up only
the pixels of the odd-numbered rows and not lighting up the pixels
of the even-numbered rows is provided, the viewing angle
characteristics may not be sufficiently improved occasionally.
However, when a general image is displayed, the display quality of
the liquid crystal display device 100A is not lowered.
[0076] In the above description, the convexed portions 152 are each
provided in correspondence with the area between the pixel areas
defined by the two pixel electrodes adjacent to each other in the
column direction, but the present invention is not limited to this.
The convexed portions 152 may be each provided in correspondence
with an area between pixel areas defined by two pixel electrodes
adjacent to each other in the row direction.
[0077] In the above description, the convexed portions 152 are each
provided in correspondence with the area between the pixel areas
defined by the two pixel electrodes 124, but the present invention
is not limited to this. The convexed portions 152 may be each
provided in correspondence with an area surrounded by pixel areas
defined by four pixel electrodes.
[0078] Hereinafter, with reference to FIG. 4, a liquid crystal
display device 100A1 will be described. In the liquid crystal
display device 100A1, the convexed portions 152 are each provided
in correspondence with the center of an area surrounded by pixel
areas defined by four pixel electrodes 124. Each convexed portion
152 partially overlaps each of the four pixel electrodes 124. When
a voltage is applied to the liquid crystal layer 160, the liquid
crystal molecules 162 are aligned in axis symmetry around the
convexed portions 152 as the centers. As can be seen, the convexed
portions 152 are alignment centers of the liquid crystal molecules
162.
[0079] In FIG. 4, the four pixel electrodes 124 arranged in two
rows by two columns are represented by reference signs 124a through
124d. In FIG. 4, among the convexed portions 152, the convexed
portion provided at the center of an area surrounded by the pixel
electrodes 124a through 124d is represented by reference sign 152a.
The convexed portion 152a is provided in correspondence with the
center of the area surrounded by the four pixel areas defined by
the four pixel electrodes 124a, 124b, 124c and 124d. Paying
attention to the convexed portion 152a, the convexed portion 152a
is provided in correspondence with one corner of each of the pixel
electrodes 124a through 124d. When a voltage is applied to the
liquid crystal layer 160, the liquid crystal molecules 162 are
aligned in axis symmetry around the convexed portion 152a as the
center. Therefore, in an area of the liquid crystal molecules 162
corresponding to the pixel electrodes 124a through 124d,
axis-symmetrical alignment centering around the convexed portion
152a is caused. Here again, it is preferable that the convexed
portion 152a is provided so as to overlap each of the pixel
electrodes 124a, 124b, 124c and 124d by 9 .mu.m or more.
[0080] In the above description, the liquid crystal display device
is of a transmissive type, but the present invention is not limited
to this. The liquid crystal display device may be of a reflective
type. For example, the pixel electrodes 124 may have a reflection
function, or a reflective member (not shown) may be provided
between the pixel electrodes 124 and the insulating plate 122.
[0081] In the above description, the convexed portions 152 are
provided on the liquid crystal layer 160 side of the counter
substrate 140, but the present invention is not limited to this.
The convexed portions 152 may be provided on the liquid crystal
layer 160 side of the active matrix substrate 120.
Embodiment 2
[0082] In the above description, as the axis-symmetrical liquid
crystal domain formation portions 150, the convexed portions 152
are provided, but the present invention is not limited to this.
Electrode-absent portions may be provided as the axis-symmetrical
liquid crystal domain formation portions 150.
[0083] Hereinafter, a liquid crystal display device in Embodiment 2
according to the present invention will be described. FIG. 5(a) is
a schematic view of a liquid crystal display device 100B in this
embodiment, and FIG. 5(b) is a schematic plan view of the liquid
crystal display device 100B. The liquid crystal display device 100E
has substantially the same structure as that of the liquid crystal
display device 100A except that the liquid crystal display device
100B includes electrode-absent portions 154 instead of the convexed
portions 152. Hence, in order to avoid redundancy, the same
descriptions will be omitted.
[0084] In the liquid crystal display device 100B, the counter
electrode 144 includes the electrode-absent portions 154. The
electrode-absent portions 154 are also called "openings". With the
liquid crystal display device 100B, in the absence of a voltage,
the liquid crystal molecules 162 in the liquid crystal layer 160
are aligned generally vertically to the main surface of the
alignment film (not shown). When a voltage is applied to the liquid
crystal layer 160, an oblique electric field is generated in
correspondence with the electrode-absent portions 154, and the
liquid crystal molecules 162 are aligned in axis symmetry around
the electrode-absent portions 154 as the centers. In this manner,
in the liquid crystal display device 100B, the electrode-absent
portions 154 are provided as the axis-symmetrical liquid crystal
domain formation portions 150.
[0085] FIG. 5(b) schematically shows pixels in the liquid crystal
display device 100B. The electrode-absent portions 154 are each
provided in correspondence with an area between pixel areas defined
by two pixel electrodes 124 adjacent to each other in the column
direction, and each electrode-absent portion 154 partially overlaps
each of the two pixel electrodes 124. When a voltage is applied to
the liquid crystal layer 160, the liquid crystal molecules 162 are
tilt-aligned in axis symmetry around the electrode-absent portions
154 as the centers. As can be seen, the electrode-absent portions
154 are alignment centers of the liquid crystal molecules 162.
[0086] In FIG. 5(b), among the two pixel electrodes 124 adjacent to
each other in the column direction, one is represented reference
sign 124a and the other is represented by reference sign 124b. In
FIG. 5(b), among the electrode-absent portions 154, the
electrode-absent portion provided in the area between the pixel
areas defined by the pixel electrodes 124a and 124b is represented
by reference sign 154a. The distance between the pixel electrodes
124a and 124b is 5 .mu.m.
[0087] In the liquid crystal display device 100B, the
electrode-absent portion 154a is provided in correspondence with
the area between the pixel areas defined by the pixel electrodes
124a and 124b, and the electrode-absent portion 154a partially
overlaps each of the pixel electrodes 124a and 124b. Herein, the
electrode-absent portion 154a is elliptical, but may be
circular.
[0088] Hereinafter, with reference to FIG. 6, the liquid crystal
display device 100B will be described. As described above, in the
liquid crystal display device 100B, the electrode-absent portion
154a is provided in correspondence with the area between the two
pixel electrodes 124a and 124b. When a prescribed voltage is
applied, the liquid crystal molecules 162 in the two pixel areas
corresponding to the pixel electrodes 124a and 124b are aligned in
axis symmetry around the electrode-absent portion 154a as the
center. Specifically, when a prescribed voltage is applied, the
liquid crystal molecules 162 corresponding to the pixel electrode
124a are aligned in correspondence with a +y side part of the
electrode-absent portion 154a, and the liquid crystal molecules 162
corresponding to the pixel electrode 124b are aligned in
correspondence with a -y side part of the electrode-absent portion
154a. In the liquid crystal display device 100B, the
electrode-absent portion 154a is the alignment center of the liquid
crystal molecules 162. In this manner, the liquid crystal molecules
162 corresponding to the two pixel electrodes 124a and 124b are
aligned around the electrode-absent portion 154a as the center, and
owing to this, the viewing angle characteristics are improved.
[0089] The electrode-absent portions 154 are elliptical and each
have a longer diameter L1 of 23 .mu.m and a shorter diameter L2 of
14 .mu.m. An overlapping width La of the electrode-absent portion
154a and the pixel electrode 124a is 9 .mu.m, and an overlapping
width Lb of the electrode-absent portion 154a and the pixel
electrode 124b is 9 .mu.m. As can be seen, the electrode-absent
portion 154a overlaps each of the pixel electrodes 124a and 124b by
9 .mu.m or more. Namely, the electrode-absent portion 154a overlaps
the two pixel electrodes 124a and 124b by a total of 18 .mu.m or
more. In this case, even when the display screen is pressed while
white is displayed, no pressing trace is left. By contrast, in the
case where the electrode-absent portion is a circle having a
diameter of 14 .mu.m, when the display screen is pressed while
white is displayed, a pressing trace may be left occasionally. From
the above, it is preferable that the electrode-absent portions 154
are each provided so as to overlap each of the pixel electrodes
124a and 124b by 9 .mu.m or more. Also in the liquid crystal
display devices 100A and 100A1 described above, it is preferable
that the convexed portions 152 are each provided so as to overlap
each of the pixel electrodes 124 by 9 .mu.m or more. The
electrode-absent portions 154 are not limited to being elliptical
or circular, and may have a different shape as long as the liquid
crystal molecules 162 can be tilt-aligned in axis symmetry.
[0090] In the above description, the electrode-absent portions 154
are each provided in correspondence with the area between the pixel
areas defined by the two pixel electrodes 124, but the present
invention is not limited to this. The electrode-absent portions 154
may be each provided in correspondence with an area surrounded by
pixel areas defined by four pixel electrodes.
[0091] In the liquid crystal display device 100B described above,
the electrode-absent portions 154 are provided on the liquid
crystal layer 160 side of the counter substrate 140, but the
present invention is not limited to this. The electrode-absent
portions 154 may be provided on the liquid crystal layer 160 side
of the active matrix substrate 120. The convexed portions 154 may
be formed in the pixel electrodes 124.
Embodiment 3
[0092] In the above description, one liquid crystal domain is
formed in one pixel, but the present invention is not limited to
this. A plurality of liquid crystal domains may be formed in one
pixel. As understood from the above description, when a voltage is
applied to the liquid crystal layer 160, axis-symmetrical liquid
crystal domains are formed around the convexed portions 152 or the
electrode-absent portions 154 as the centers. Hence, in the
following description, the convexed portions 152 and the
electrode-absent portions 154 may be collectively referred to as
the "axis-symmetrical liquid crystal domain formation portions 150"
or the "domain formation portions 150" occasionally.
[0093] Hereinafter, with reference to FIG. 7, a liquid crystal
display device in Embodiment 3 according to the present invention
will be described. FIG. 7 is a schematic view of a liquid crystal
display device 100C in this embodiment. The liquid crystal display
device 100C has substantially the same structure as that of the
liquid crystal display device 100A except that a plurality of
liquid crystal domains are formed in one pixel in the liquid
crystal display device 100C. Hence, in order to avoid redundancy,
the same descriptions will be omitted.
[0094] In the liquid crystal display device 100C, the gate lines G
are each provided in correspondence with an area between the pixel
electrodes 124 of two rows adjacent to each other, and the domain
formation portions 150 are provided so as to overlap the gate lines
G. Storage capacitance lines CS each overlap the pixel electrodes
124 of one of the two rows adjacent to each other. Herein, the
storage capacitance lines CS are each provided so as to overlap the
centers of the pixel electrodes 124. For example, the pixel
electrodes 124 each have a length of 30 .mu.m in the x direction
and a length of 90 .mu.m in the y direction.
[0095] In FIG. 7, three pixel electrodes 124 sequentially arranged
in the column direction are represented by reference signs 124a,
124b and 124c. In FIG. 7, among the domain formation portions 150,
the domain formation portion provided in correspondence with an
area between the pixel electrodes 124a and 124b is represented by
reference sign 150a, and the domain formation portion provided in
correspondence with an area between the pixel electrodes 124b and
124c is represented by reference sign 150b.
[0096] Paying attention to the pixel electrode 124b, the domain
formation portions 150a and 150b are provided in correspondence
with the pixel electrode 124b. The domain formation portion 150a is
provided so as to overlap one edge of the pixel electrode 124b, and
the domain formation portion 150b is provided so as to overlap the
other edge of the pixel electrode 124b.
[0097] FIG. 8 is a schematic enlarged view of the liquid crystal
display device 100C. In an area corresponding to the pixel
electrode 124b, liquid crystal domains centering around the domain
formation portions 150a and 150b are formed. Specifically, two
areas 124b1 and 124b2 are defined by the pixel electrode 124b. In
the area 124b1, the liquid crystal domain centering around the
domain formation portion 150a is formed; and in the area 124b2, the
liquid crystal domain centering around the domain formation portion
150b is formed. Therefore, when the entirety of the pixel electrode
124b is seen, the liquid crystal molecules 162 corresponding to the
pixel electrode 124 are tilt-aligned in almost all the azimuths.
Owing to this, the viewing angle characteristics are improved.
[0098] In the liquid crystal domain formed in correspondence with
the pixel electrode 124b, a disclination line is formed between the
domain formation portions 150a and 150b. The disclination line is
formed in an area corresponding to a line which equally divides a
line segment connecting the domain formation portions 150a and
150b. In the liquid crystal display device 100C, the storage
capacitance line CS is provided so as to overlap the disclination
line. Therefore, the disclination line does not substantially
contribute the decrease in the numerical aperture.
[0099] In the above description, the pixel electrodes 124 have a
uniform width, but the present invention is not limited to this.
The width of the pixel electrodes 124 may be varied.
[0100] As shown in FIG. 9, in a liquid crystal display device
100C1, the pixel electrodes 124 each include a unit electrode
124u1, a unit electrode 124u2 and a connection section 124s for
connecting the unit electrode 124u1 and the unit electrode 124u2.
The connection section 124s has a length in the x direction which
is shorter than that of each of the unit electrode 124u1 and
124u2.
[0101] With the liquid crystal display device 100C1, when a voltage
is applied to the liquid crystal layer 160, the liquid crystal
molecules 162 corresponding to the unit electrode 124u1 are
tilt-aligned in axis symmetry around the domain formation portion
150a as the center, and the liquid crystal molecules 162
corresponding to the unit electrode 124u2 are tilt-aligned in axis
symmetry around the domain formation portion 150b as the center. As
can be seen, since the length of the connection section 124s of the
pixel electrode 124 in the x direction is shorter than that of each
of the unit electrode 124u1 and 124u2, the liquid crystal molecules
162 corresponding to the unit electrodes 124u1 and 124u2 are
aligned in accordance with the oblique electric field. Owing to
this, the response speed and the alignment stability can be
improved. Especially in the case where the length of the pixel
electrode 124 in the y direction is relatively longer than the
length thereof in the x direction, the length of each of the unit
electrodes 124u1 and 124u2 in the y direction can be made generally
equal to the length thereof in the x direction. Therefore, the
response speed and the alignment stability can be further
improved.
[0102] In the liquid crystal display devices 100C and 100C1
described above, the storage capacitance lines CS are provided so
as to overlap the centers of the pixel electrodes 124, but the
present invention is not limited to this. As shown in FIG. 10, in a
liquid crystal display device 100C2, the storage capacitance lines
CS may be provided so as to overlap portions, other than the
centers, of the pixel electrodes 124.
[0103] In the above description, the gate lines G are provided so
as to overlap the domain formation portions 150 provided between
the pixel electrodes 124 of the two rows adjacent to each other and
the storage capacitance lines CS are provided so as to overlap the
pixel electrodes 124, but the present invention is not limited to
this. The storage capacitance lines CS may be provided so as to
overlap the domain formation portions 150 located between the pixel
electrodes 124 of two rows adjacent to each other and the gate
lines G may be provided so as to overlap the pixel electrodes
124.
[0104] As described above, one type of lines among the gate lines G
and the storage capacitance lines CS may be provided so as to
overlap the domain formation portions 150 located between two rows
adjacent to each other in the column direction, and the other type
of lines among the gate lines G and the storage capacitance lines
CS may be provided so as to overlap the pixel electrodes. It is
preferable that the other type of lines are provided so as to
overlap the borderline between different axis-symmetrical
tilt-alignment regions which are provided by the domain formation
portions 150a and 150b located in correspondence with two pixel
electrodes adjacent to each other in the column direction (for
example, the pixel electrodes 124a and 124b).
[0105] In the liquid crystal display devices 100C, 100C1 and 100C2
described above, the domain formation portions 150 are each
provided in correspondence with the area between the two pixel
electrodes 124, but the present invention is not limited to this.
The domain formation portions 150 may be each provided in
correspondence with an area surrounded by four pixel electrodes
124.
[0106] Hereinafter, with reference to FIG. 11, a liquid crystal
display device 100C3 will be described. In the liquid crystal
display device 100C3, the domain formation portions 150 are each
provided in correspondence with the center of an area surrounded by
pixel areas defined by four pixel electrodes 124. Each domain
formation portion 150 partially overlaps each of the four pixel
electrodes 124. When a voltage is applied to the liquid crystal
layer 160, the liquid crystal molecules 162 are aligned in axis
symmetry around the closest domain formation portions 150 as the
centers. As can be seen, the domain formation portions 150 are
alignment centers of the liquid crystal molecules 162.
[0107] In FIG. 11, among six pixel electrodes 124 arranged in three
rows by two columns, the pixel electrodes located at the upper left
position, the upper right position, the center left position, the
center right position, the lower left position and the lower right
position are respectively represented by reference signs 124a
through 124f. In FIG. 11, among the domain formation portions 150,
the domain formation portion provided in correspondence with the
center of an area surrounded by the four pixel electrodes 124a,
124b, 124c and 124d is represented by reference sign 150a, and the
domain formation portion provided in correspondence with the center
of an area surrounded by the four pixel electrodes 124c, 124d, 124e
and 124f is represented by reference sign 150b.
[0108] Paying attention to the pixel electrode 124c, the domain
formation portions 150a and 150b are respectively provided in
correspondence with two corners of the pixel electrode 124c. When a
voltage is applied to the liquid crystal layer 160, in an area of
the liquid crystal layer 160 which corresponds to the pixel
electrode 124c, a part of axis-symmetrical alignment centering
around the domain formation portion 150a and a part of
axis-symmetrical alignment centering around the domain formation
portion 150b are formed. More precisely, a disclination line may be
formed occasionally in an area corresponding to a line which
equally divides a line segment connecting the domain formation
portions 150a and 150b. The storage capacitance lines CS extend in
the x direction through the centers of the pixel electrodes 124 so
as to overlap the disclination line, and thus efficiently suppress
the decrease in the numerical aperture.
[0109] In the above description, the liquid crystal display device
is of a transmissive type, but the present invention is not limited
to this. The liquid crystal display device may be of a reflective
type. For example, the pixel electrodes 124 may have a reflection
function, or a reflective member (not shown) may be provided
between the pixel electrodes 124 and the insulating plate 122.
Alternatively, the liquid crystal display device may be of a
transreflective type.
[0110] Hereinafter, with reference to FIG. 12, the liquid crystal
display device 100C4 will be described. The liquid crystal display
device 100C4 is of a transreflective type.
[0111] In the liquid crystal display device 100C4, pixel areas
defined by the pixel electrodes 124 each include a transmissive
region 124t and a reflective region 124r. In the liquid crystal
display device 100C4, the domain formation portions 150 are each
provided in correspondence with an area between pixel areas defined
by two pixel electrodes 124 adjacent to each other in the column
direction.
[0112] In FIG. 12, three pixel electrodes 124 sequentially arranged
in the column direction are represented by reference signs 124a
through 124c. The transmissive regions and the reflective regions
corresponding to the pixel electrodes 124a through 124c are
respectively represented by 124at through 124ct and 124ar through
124cr. Among the domain formation portions 150, the domain
formation portion provided in an area between the pixel electrodes
124a and 124b is represented by reference sign 150a, and the domain
formation portion provided in an area between the pixel electrodes
124b and 124c is represented by reference sign 150b.
[0113] In the liquid crystal display device 100C4, the reflective
region 124ar corresponding to the pixel electrode 124a and the
reflective region 124br corresponding to the pixel electrode 124b
are adjacent to each other. The domain formation portion 150a is
provided in an area between the reflective region 124ar and the
reflective region 124br, and the domain formation portion 150b is
provided in an area between the transmissive region 124bt and the
transmissive region 124ct.
[0114] When a voltage is applied to the liquid crystal layer 160,
the liquid crystal molecules 162 corresponding to the reflective
region 124ar and the reflective region 124br are aligned in axis
symmetry around the domain formation portion 150a as the center.
When a voltage is applied to the liquid crystal layer 160, the
liquid crystal molecules 162 corresponding to the transmissive
regions 124bt and 124ct are aligned in axis symmetry around the
domain formation portion 150b as the center. In this manner, in the
liquid crystal display device 100C4, liquid crystal domains, each
centering around the domain formation portion 150 provided in
correspondence with the area between the transmissive regions 124t
of two pixel electrodes 124 or in correspondence with the area
between the reflective regions 124r of two pixel electrodes 124,
are formed.
[0115] In the liquid crystal display device 100C4, the domain
formation portions 150 are each provided in correspondence with the
area between the two pixel electrodes, but the present invention is
not limited to this. The domain formation portions 150 may be each
provided in correspondence with an area surrounded by four pixel
electrodes.
[0116] Hereinafter, with reference to FIG. 13, a liquid crystal
display device 100C5 will be described. In the liquid crystal
display device 100C5, pixel areas defined by the pixel electrodes
124 each include a transmissive region 124t and a reflective region
124r. In the liquid crystal display device 100C5, the domain
formation portions 150 are each provided in correspondence with an
area surrounded by pixel areas defined by four pixel electrodes 124
arranged in two rows by two columns.
[0117] In FIG. 13, among six pixel electrodes 124 arranged in three
rows by two columns, the pixel electrodes located at the upper left
position, the upper right position, the center left position, the
center right position, the lower left position and the lower right
position are respectively represented by reference signs 124a
through 124f. In FIG. 13, among the domain formation portions 150,
the domain formation portion provided in correspondence with an
area surrounded by pixel areas defined by the pixel electrodes 124a
through 124d is represented by reference sign 150a, and the domain
formation portion provided in correspondence with an area
surrounded by pixel areas defined by the pixel electrodes 124c
through 124f is represented by reference sign 150b. The
transmissive regions corresponding to the pixel electrodes 124a
through 124f are respectively represented by 124at through 124ft.
The reflective regions corresponding to the pixel electrodes 124a
through 124f are respectively represented by 124ar through
124fr.
[0118] In the liquid crystal display device 100C5, the reflective
regions 124ar through 124dr corresponding to the pixel electrodes
124a through 124d face each other, and the domain formation portion
150a is provided so as to overlap a part of each of the reflective
regions 124ar through 124dr. Similarly, the transmissive regions
124ct through 124ft corresponding to the pixel electrodes 124c
through 124f face each other, and the domain formation portion 150b
is provided so as to overlap a part of each of the transmissive
regions 124ct through 124ft. When a voltage is applied to the
liquid crystal layer 160, the liquid crystal molecules 162
corresponding to the reflective regions 124ar through 124dr are
aligned in axis symmetry around the domain formation portion 150a
as the center. When a voltage is applied to the liquid crystal
layer 160, the liquid crystal molecules 162 corresponding to the
transmissive regions 124ct through 124ft are aligned in axis
symmetry around the domain formation portion 150b as the
center.
[0119] In this manner, in the liquid crystal display device 100C5,
a liquid crystal domain, centering around the domain formation
portion 150a surrounded by the reflective regions 124ar through
124dr corresponding to the pixel electrodes 124a through 124d, is
formed. Another liquid crystal domain, centering around the domain
formation portion 150b surrounded by the transmissive regions 124ct
through 124ft corresponding to the pixel electrodes 124c through
124f, is formed.
Embodiment 4
[0120] In the above description, the liquid crystal display device
is of a CPA mode, but the present invention is not limited to this.
The liquid crystal display device may be of another mode.
[0121] Hereinafter, a liquid crystal display device in Embodiment 4
according to the present invention will be described. FIG. 14(a) is
a schematic view of a liquid crystal display device 100D in this
embodiment, and FIG. 14(b) is a schematic plan view of the liquid
crystal display device 100D. The liquid crystal display device 100D
does not include the axis-symmetrical domain formation portions 150
and has substantially the same structure as that of the liquid
crystal display device 100A except for the shape of the pixel
electrodes 124. Hence, in order to avoid redundancy, the same
descriptions will be omitted.
[0122] In the liquid crystal display device 100D, the pixel
electrodes 124 each include a trunk electrode 124j and a plurality
of linear electrodes 124k extending parallel to each other in each
of directions d1 through d4 from the trunk electrode 124j.
[0123] The active matrix substrate 120 and the counter substrate
140 each include an alignment film and a polarizer plate, neither
of which is shown. The polarization axes of the polarizer plates
extend in the x axis direction and the y axis direction, and have a
crossed Nicols relationship.
[0124] In FIG. 14(b), among two pixel electrodes 124 adjacent to
each other in the column direction, one is represented by reference
sign 124a and the other is represented by reference sign 124b. The
pixel electrode 124b is line-symmetrical to the pixel electrode
124a with respect to the x axis direction and the y axis direction,
and is generally point-symmetrical to the pixel electrode 124a.
[0125] The pixel electrode 124a includes a trunk electrode 124aj, a
plurality of linear electrodes 124k1 extending parallel to each
other in the direction d1 from the trunk electrode 124aj, and a
plurality of linear electrodes 124k2 extending parallel to each
other in the direction d2, crossing perpendicularly the direction
d1, from the trunk electrode 124aj. The pixel electrode 124b
includes a trunk electrode 124bj, a plurality of linear electrodes
124k3 extending parallel to each other in the direction d3,
antiparallel to the direction d2, from the trunk electrode 124bj,
and a plurality of linear electrodes 124k4 extending parallel to
each other in the direction d4, antiparallel to the direction d1,
from the trunk electrode 124bj. Here, it is set that the horizontal
direction (left-right direction) of the display screen (the plane
of the sheet of FIG. 14(b)) is the reference direction on which the
azimuth angle direction is measured, and the counterclockwise
direction is the forward direction (considering that the display
screen is the face of the clock, the 3 o'clock direction is the
azimuth angle of 0.degree. and the counterclockwise direction is
the forward direction). With such settings, the directions d1
through d4 are 135.degree., 45.degree., 225.degree. and
315.degree., respectively. The trunk electrodes 124aj and 124bj
extend only in the y direction and do not extend in the x
direction.
[0126] For example, in the pixel electrodes 124a and 124b, the
trunk electrodes 124aj and 124bj each have a width of 3 .mu.m. The
linear electrodes 124k1, 124k2, 124k3 and 124k4 each have a width
of 3 .mu.m, and the distance therebetween is 3 .mu.m. The trunk
electrode 124aj of the pixel electrode 124a is provided on the same
straight line as the trunk electrode 124bj of the pixel electrode
124b.
[0127] The liquid crystal layer 160 is of a vertical alignment
type. The liquid crystal layer 160 includes a liquid crystal domain
A formed by the linear electrodes 124k1 of the pixel electrode
124a, a liquid crystal domain B formed by the linear electrodes
124k2 of the pixel electrode 124a, a liquid crystal domain C formed
by the linear electrodes 124k3 of the pixel electrode 124b, and a
liquid crystal domain D formed by the linear electrodes 124k4 of
the pixel electrode 124b. When no voltage is applied to the liquid
crystal layer 160 or when the voltage applied thereto is relatively
low, the liquid crystal molecules 162 are aligned vertically to a
main surface of the alignment film (not shown) except for in the
vicinity of the pixel electrodes 124. By contrast, when a
prescribed voltage is applied to the liquid crystal layer 160, the
liquid crystal molecules 162 are aligned in the directions d1
through d4 in which the linear electrodes 124k1, 124k2, 124k3 and
124k4 extend.
[0128] In this specification, the alignment direction of the liquid
crystal molecules at the center of each of the liquid crystal
domains A through D is referred to as the "reference alignment
direction". Among the reference alignment directions, an azimuth
angle component of a direction from the rear side to the front side
along the longer axis of the liquid crystal molecules (namely, the
azimuth angle component of the liquid crystal molecules projected
on the main surface of the alignment film) is referred to as the
"reference alignment azimuth". The reference alignment azimuth
characterizes the corresponding liquid crystal domain and
dominantly influences the viewing angle characteristics of the
respective liquid crystal domain. Where the horizontal direction
(left-right direction) of the display screen (the plane of the
sheet of FIG. 14(b)) is the reference direction on which the
azimuth angle direction is measured and the counterclockwise
direction is the forward direction, the reference alignment
azimuths of the four liquid crystal domains A through D are set
such that the difference between two random azimuths out of these
four azimuths is generally equal to an integral multiple of
90.degree.. Specifically, the reference alignment azimuths of the
liquid crystal domains A, B, C and D are 135.degree., 45.degree.,
225.degree. and 315.degree., respectively. In this manner, the
liquid crystal molecules 162 are aligned in four different
directions d1 through d4, and owing to this, the viewing angle
characteristics are improved.
[0129] Paying attention to a plane including a straight line along
the trunk electrodes 124aj and 124bj of the pixel electrodes 124a
and 124b, in the presence of a voltage, the liquid crystal
molecules 162 are aligned symmetrically with respect to this plane.
The liquid crystal molecules 162 are aligned around the center of
the area between the pixel areas defined by the pixel electrodes
124a and 124b as the center. In the liquid crystal display device
100D, the center of alignment is at the center of the area between
the pixel areas defined by the pixel electrodes 124a and 124b.
[0130] Hereinafter, advantages of the liquid crystal display device
100D in this embodiment will be described in comparison with a
liquid crystal display device in Comparative Example 2. First, with
reference to FIG. 15, a liquid crystal display device 900 in
Comparative Example 2 will be described. FIG. 15(a) is a schematic
view of the liquid crystal display device 900, and FIG. 15(b) is a
plan view of the liquid crystal display device 900. Pixel
electrodes 924 of the liquid crystal display device 900 each
correspond to a combination of the pixel electrodes 124a and
124b.
[0131] In the liquid crystal display device 900, the pixel
electrodes 924 each include a cross-shaped trunk electrode 924j and
linear electrodes 924k1 through 924k4 extending in each of four
different directions d1 through d4 from the trunk electrode 924j.
When a voltage is applied to a liquid crystal layer 960 in the
liquid crystal display device 900, liquid crystal molecules 962 in
the vicinity of the linear electrodes 924k are aligned parallel to
the directions in which the linear electrodes 924k extend, whereas
the liquid crystal molecules 962 in the vicinity of the trunk
electrode 924j are aligned parallel to the directions in which the
trunk electrode 924j extends. Therefore, the luminance in the
vicinity of the linear electrodes 924k is relatively high, whereas
the luminance in the vicinity of the trunk electrode 924j is
relatively low. With the liquid crystal display device 900 in such
a state, even when the size of the trunk electrode 924j is
decreased in accordance with the decrease in the size of the pixel
electrode 924, the size of the trunk electrode 924j cannot be
decreased to a level less than the production limit. Therefore, the
ratio of the area in the vicinity of the trunk electrode 924j of
the lower luminance is increased, and so the luminance of the
liquid crystal display device 900 is significantly lowered.
[0132] By contrast, in the liquid crystal display device 100D, the
trunk electrodes 124aj and 124bj extend only in the y direction and
do not extend in the x direction. Therefore, with the liquid
crystal display device 100D, even when the size of the pixel area
is decreased, the ratio of the area of the trunk electrode with
respect to the pixel area is low, and so the liquid crystal display
device 100D can suppress the reduction in the luminance.
[0133] In the liquid crystal display device 900 in Comparative
Example 2, symmetrical viewing angle characteristics are realized
in each pixel. By contrast, in the liquid crystal display device
100D, symmetrical viewing angle characteristics are realized in
every other pixels. Therefore, with the liquid crystal display
device 100D, when, for example, special display of lighting up only
the pixels of the odd-numbered rows and not lighting up the pixels
of the even-numbered rows is provided, the viewing angle
characteristics may not be sufficiently improved occasionally.
However, when a general image is displayed, the display quality of
the liquid crystal display device 100D is not lowered. In the
liquid crystal display device 900 in Comparative Example 2, it is
preferable that the storage capacitance lines CS are each provided
along the centers of the pixel electrodes 924 so as to overlap a
portion of the trunk electrode 924j extending in the x direction.
By contrast, in the liquid crystal display device 100D, the trunk
electrodes 124j do not have a portion extending in the x direction.
Therefore, the storage capacitance lines CS may be each provided at
any position between gate lines G adjacent to each other. As shown
in FIG. 16, in a liquid crystal display device 100D1, the storage
capacitance lines CS may be each provided so as to overlap
portions, other than the centers, the pixel electrodes 124.
[0134] In the above description, the four different reference
alignment directions of the liquid crystal molecules 162 are
realized by the two pixel electrodes 124, but the present invention
is not limited to this. The four different reference alignment
directions of the liquid crystal molecules 162 may be realized by
four pixel electrodes.
[0135] Hereinafter, with reference to FIG. 17, a liquid crystal
display device 100D2 will be described. In FIG. 17, four pixel
electrodes arranged in two rows by two columns are respectively
represented as pixel electrodes 124a through 124d. The pixel
electrode 124b is generally line-symmetrical to the pixel electrode
124a with respect to the y axis direction, and the pixel electrode
124c is generally line-symmetrical to the pixel electrode 124a with
respect to the x axis direction. The pixel electrode 124d is
generally point-symmetrical to the pixel electrode 124a.
[0136] The pixel electrode 124a includes a trunk electrode 124aj
and a plurality of linear electrodes 124k1 extending parallel to
each other in the direction d1 from the trunk electrode 124aj. The
pixel electrode 124b includes a trunk electrode 124bj and a
plurality of linear electrodes 124k2 extending parallel to each
other in the direction d2, crossing perpendicularly the direction
d1, from the trunk electrode 124bj. The pixel electrode 124c
includes a trunk electrode 124cj and a plurality of linear
electrodes 124k3 extending parallel to each other in the direction
d3, antiparallel to the direction d2, from the trunk electrode
124cj. The pixel electrode 124d includes a trunk electrode 124dj
and a plurality of linear electrodes 124k4 extending parallel to
each other in the direction d4, antiparallel to the direction d1,
from the trunk electrode 124dj.
[0137] In the liquid crystal display device 100D2, the liquid
crystal layer 160 includes a liquid crystal domain A formed by the
pixel electrode 124a, a liquid crystal domain B formed by the pixel
electrode 124b, a liquid crystal domain C formed by the pixel
electrode 124c, and a liquid crystal domain D formed by the pixel
electrode 124d. When a voltage is applied to the liquid crystal
layer 160, the liquid crystal molecules 162 corresponding to the
pixel electrode 124a are aligned in the direction d1, and the
liquid crystal molecules 162 corresponding to the pixel electrode
124b are aligned in the direction d2. Similarly, the liquid crystal
molecules 162 corresponding to the pixel electrode 124c are aligned
in the direction d3, and the liquid crystal molecules 162
corresponding to the pixel electrode 124d are aligned in the
direction d4. The liquid crystal molecules 162 are aligned around
the center of an area surrounded by pixel areas defined by the
pixel electrodes 124a through 124d as the center. In the liquid
crystal display device 100D2, the center of alignment is at the
center of the area surrounded by the pixel areas defined by the
pixel electrodes 124a through 124d. In this manner, the liquid
crystal molecules 162 are aligned in the four different directions
d1 through d4, and owing to this, the viewing angle characteristics
are improved.
[0138] The disclosure of Japanese Patent Application No. 2009-4093,
based upon which the present application claims the benefit of
priority, is incorporated herein by reference.
INDUSTRIAL APPLICABILITY
[0139] The present invention can provide a liquid crystal display
device realizing a high luminance. Such a liquid crystal display
device is preferably usable for mobile phones and game
machines.
REFERENCE SIGNS LIST
[0140] 100 Liquid crystal display device [0141] 120 Active matrix
substrate [0142] 122 Insulating plate [0143] 124 Pixel electrode
[0144] 140 Counter substrate [0145] 142 Insulating plate [0146] 144
Counter electrode [0147] 150 Axis symmetrical liquid crystal domain
formation portion [0148] 152 Convexed portion [0149] 154
Electrode-absent portion [0150] 160 Liquid crystal layer [0151] 162
Liquid crystal molecules
* * * * *